1. Field of the Invention
The present invention relates to a vehicle steering control apparatus and, more particularly, to a vehicle steering control apparatus which assists a steering effort so that a moving line of the vehicle matches a target moving line.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Laid-Open Patent Application No. 7-104856, an apparatus for generating a steering force, when an actual moving line of a vehicle deviates from a previously determined moving line (hereinafter referred to as a predetermined line), so that the vehicle is moved in a direction in which the actual moving line is shifted closer to the predetermined line. The above-mentioned conventional apparatus has a mechanism for detecting a range of a lane on which the vehicle is moving and a mechanism for detecting a range of area in which the vehicle is moving in the lane. Additionally, the above-mentioned apparatus has a mechanism for generating a steering torque so as to return the vehicle to a middle of the lane when the vehicle is shifted toward a side of the lane. Hereinafter, this steering torque is referred to as a returning steering torque.
According to the above-mentioned apparatus, when the moving line of the vehicle deviates from the predetermined line, such a situation can be conveyed to a driver of the vehicle by generating a returning steering torque. Additionally, the driver of the vehicle provided with the above-mentioned conventional apparatus can easily return the vehicle to the predetermined line by being assisted by the returning steering torque. Thus, according to the above-mentioned conventional apparatus, the vehicle can be easily and safely maintained to move on the predetermined line
Generally, a moving line which provides a comfortable feel to a driver differs from driver to driver. However, in the above-mentioned conventional apparatus, a fixed line is always set without consideration of such difference among individuals. In the above-mentioned conventional apparatus, the returning steering torque may act to resist a steering effort by the driver when a moving line desired by the driver does not match the predetermined line. In this respect, the above-mentioned conventional apparatus is not always optimum in assisting a steering effort by a driver.
Additionally, the above-mentioned conventional apparatus can alert the driver by automatically generating a returning steering torque when the vehicle is shifted to a side of the-lane on which the vehicle is moving due to some reasons. Thus, according to the above-mentioned conventional apparatus, the vehicle is prevented from deviating from the lane in which the vehicle should be maintained. However, there may be an obstacle such as a motorcycle on the lane. In such a case, the vehicle must move a side of the lane so as to avoid the obstacle. However, the above-mentioned conventional apparatus generates a returning steering torque so as to return the vehicle to the middle of the lane. Accordingly, the driver of the vehicle is required to make a steering effort to resist the returning steering force when an attempt is made to move along a side of the lane so as to avoid an obstacle. Thus, the above-mentioned conventional apparatus may provide a difficulty in maintaining movement of a vehicle along a side of a lane when the vehicle must move the side of the lane so as to avoid an obstacle.
As mentioned above, the conventional apparatus has a problem in that a driver cannot control a vehicle to move a desired line within a lane in which the vehicle is moving since the conventional apparatus always generates a steering torque to maintain the vehicle on a fixed line or always generates a steering torque proportional to a distance between the fixed line and the vehicle.